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 * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.lang;

import java.util.Objects;

/**
 * An element in a stack trace, as returned by {@link
 * Throwable#getStackTrace()}.  Each element represents a single stack frame.
 * All stack frames except for the one at the top of the stack represent
 * a method invocation.  The frame at the top of the stack represents the
 * execution point at which the stack trace was generated.  Typically,
 * this is the point at which the throwable corresponding to the stack trace
 * was created.
 *
 * @author Josh Bloch
 * @since 1.4
 */
public final class StackTraceElement implements java.io.Serializable {

  // Normally initialized by VM (public constructor added in 1.5)
  private String declaringClass;
  private String methodName;
  private String fileName;
  private int lineNumber;

  /**
   * Creates a stack trace element representing the specified execution
   * point.
   *
   * @param declaringClass the fully qualified name of the class containing the execution point
   * represented by the stack trace element
   * @param methodName the name of the method containing the execution point represented by the
   * stack trace element
   * @param fileName the name of the file containing the execution point represented by the stack
   * trace element, or {@code null} if this information is unavailable
   * @param lineNumber the line number of the source line containing the execution point represented
   * by this stack trace element, or a negative number if this information is unavailable. A value
   * of -2 indicates that the method containing the execution point is a native method
   * @throws NullPointerException if {@code declaringClass} or {@code methodName} is null
   * @since 1.5
   */
  public StackTraceElement(String declaringClass, String methodName,
      String fileName, int lineNumber) {
    this.declaringClass = Objects.requireNonNull(declaringClass, "Declaring class is null");
    this.methodName = Objects.requireNonNull(methodName, "Method name is null");
    this.fileName = fileName;
    this.lineNumber = lineNumber;
  }

  /**
   * Returns the name of the source file containing the execution point
   * represented by this stack trace element.  Generally, this corresponds
   * to the {@code SourceFile} attribute of the relevant {@code class}
   * file (as per <i>The Java Virtual Machine Specification</i>, Section
   * 4.7.7).  In some systems, the name may refer to some source code unit
   * other than a file, such as an entry in source repository.
   *
   * @return the name of the file containing the execution point represented by this stack trace
   * element, or {@code null} if this information is unavailable.
   */
  public String getFileName() {
    return fileName;
  }

  /**
   * Returns the line number of the source line containing the execution
   * point represented by this stack trace element.  Generally, this is
   * derived from the {@code LineNumberTable} attribute of the relevant
   * {@code class} file (as per <i>The Java Virtual Machine
   * Specification</i>, Section 4.7.8).
   *
   * @return the line number of the source line containing the execution point represented by this
   * stack trace element, or a negative number if this information is unavailable.
   */
  public int getLineNumber() {
    return lineNumber;
  }

  /**
   * Returns the fully qualified name of the class containing the
   * execution point represented by this stack trace element.
   *
   * @return the fully qualified name of the {@code Class} containing the execution point
   * represented by this stack trace element.
   */
  public String getClassName() {
    return declaringClass;
  }

  /**
   * Returns the name of the method containing the execution point
   * represented by this stack trace element.  If the execution point is
   * contained in an instance or class initializer, this method will return
   * the appropriate <i>special method name</i>, {@code <init>} or
   * {@code <clinit>}, as per Section 3.9 of <i>The Java Virtual
   * Machine Specification</i>.
   *
   * @return the name of the method containing the execution point represented by this stack trace
   * element.
   */
  public String getMethodName() {
    return methodName;
  }

  /**
   * Returns true if the method containing the execution point
   * represented by this stack trace element is a native method.
   *
   * @return {@code true} if the method containing the execution point represented by this stack
   * trace element is a native method.
   */
  public boolean isNativeMethod() {
    return lineNumber == -2;
  }

  /**
   * Returns a string representation of this stack trace element.  The
   * format of this string depends on the implementation, but the following
   * examples may be regarded as typical:
   * <ul>
   * <li>
   * {@code "MyClass.mash(MyClass.java:9)"} - Here, {@code "MyClass"}
   * is the <i>fully-qualified name</i> of the class containing the
   * execution point represented by this stack trace element,
   * {@code "mash"} is the name of the method containing the execution
   * point, {@code "MyClass.java"} is the source file containing the
   * execution point, and {@code "9"} is the line number of the source
   * line containing the execution point.
   * <li>
   * {@code "MyClass.mash(MyClass.java)"} - As above, but the line
   * number is unavailable.
   * <li>
   * {@code "MyClass.mash(Unknown Source)"} - As above, but neither
   * the file name nor the line  number are available.
   * <li>
   * {@code "MyClass.mash(Native Method)"} - As above, but neither
   * the file name nor the line  number are available, and the method
   * containing the execution point is known to be a native method.
   * </ul>
   *
   * @see Throwable#printStackTrace()
   */
  public String toString() {
    return getClassName() + "." + methodName +
        (isNativeMethod() ? "(Native Method)" :
            (fileName != null && lineNumber >= 0 ?
                "(" + fileName + ":" + lineNumber + ")" :
                (fileName != null ? "(" + fileName + ")" : "(Unknown Source)")));
  }

  /**
   * Returns true if the specified object is another
   * {@code StackTraceElement} instance representing the same execution
   * point as this instance.  Two stack trace elements {@code a} and
   * {@code b} are equal if and only if:
   * <pre>{@code
   *     equals(a.getFileName(), b.getFileName()) &&
   *     a.getLineNumber() == b.getLineNumber()) &&
   *     equals(a.getClassName(), b.getClassName()) &&
   *     equals(a.getMethodName(), b.getMethodName())
   * }</pre>
   * where {@code equals} has the semantics of {@link
   * java.util.Objects#equals(Object, Object) Objects.equals}.
   *
   * @param obj the object to be compared with this stack trace element.
   * @return true if the specified object is another {@code StackTraceElement} instance representing
   * the same execution point as this instance.
   */
  public boolean equals(Object obj) {
    if (obj == this) {
      return true;
    }
    if (!(obj instanceof StackTraceElement)) {
      return false;
    }
    StackTraceElement e = (StackTraceElement) obj;
    return e.declaringClass.equals(declaringClass) &&
        e.lineNumber == lineNumber &&
        Objects.equals(methodName, e.methodName) &&
        Objects.equals(fileName, e.fileName);
  }

  /**
   * Returns a hash code value for this stack trace element.
   */
  public int hashCode() {
    int result = 31 * declaringClass.hashCode() + methodName.hashCode();
    result = 31 * result + Objects.hashCode(fileName);
    result = 31 * result + lineNumber;
    return result;
  }

  private static final long serialVersionUID = 6992337162326171013L;
}
